As technology progresses, portable devices tend to integrate more features. For example, portable devices may include features associated with personal digital assistants (PDAs), cellular telephones, wireless internet access devices, music players, such as MP3 players, global positioning system (GPS) receivers, and the like. Such portable devices may support one or more wireless communications protocols, such as third (3G), fourth (4G), or later generation cellular telephone protocols, GPS protocols, wireless fidelity (Wi-Fi) protocols, Bluetooth®, and the like.
Some wireless communications protocols send a reference timing signal embedded in an RF signal to a portable device for the purpose of correcting internal clock signals within the portable device. These corrected internal clock signals may be used to provide frequency-accurate transmit signals from the portable device, or may be used in frequency-accurate applications, such as GPS navigation. Generating frequency-corrected clock signals may require frequency synthesizer circuitry, which may have significant power requirements when enabled. Therefore, disabling the frequency synthesizer circuitry may be desirable when frequency-corrected clock signals are not needed, particularly in battery-powered devices.
System circuitry may need a frequency-corrected clock signal for certain applications, such as wireless communications, and may get by with a non-frequency-corrected clock signal for other applications, such as playing music. Thus, there is a need for clock circuitry that can provide a system clock signal that is frequency-corrected when needed and is not frequency-corrected when not needed to reduce power consumption, reduce noise, or the like.